This invention relates to novel alloys and molds fabricated therefrom that are intended for use in the molding of fire resistant plastic articles.
By way of example, injection molding generally is an intermittent, cyclic process in which particles of plastic material containing a "blowing agent" incorporated therein are heated until they soften. The resulting mass is then forced into a closed mold at pressures of, for example, from 10,000 to 20,000 p.s.i., wherein it solidifies to form a solid article shaped in the reverse image of the mold.
Practically any thermoplastic material can be molded. Both branched and linear polyethylene as well as formulations of poly(vinyl chloride), polystyrenes and polyurethanes are now being used in commercial quantities in the manufacture of containers, toys, and household and industrial products by injection molding. In making fire resistant articles, such as television cabinets, fire retardant materials are incorporated with the thermoplastic material. Such fire retardant materials usually contain bromine, chloride or antimony oxide compounds and are corrosive as are some of their decomposition products.
As a consequence, molds and dies must be resistant to this corrosive action. Existing mold materials which are so resistant are unable, however, when cast to reproduce the detail required.
Attempts to obtain pattern detail completely and accurately while at the same time making the molds and dies immune to the corrosive action of the fumes formed during formation of the fire retardant plastic articles have, up to now, not been successful.